Microbial activity and accumulation of organic matter in the burrow of the mud shrimp, Upogebia major (Crustacea: Thalassinidea)

Abstract

Microbial activity and accumulation of organic matter in the burrow of the thalassinidean mud shrimp, Upogebia major, were studied on a tidal flat along the northern coast of Tokyo Bay, Japan. The burrow of U. major is Y-shaped with an upper U-shaped part plus a lower I-shaped part. Its lower part can extend to a depth of 2 m. In the present study, we compare electron transport system activity (ETSA), bacterial abundance and organic matter content [total organic carbon (TOC), total nitrogen (TN) and chlorophyll a (chl. a)] of the burrow wall sediment with the tidal flat surface and non-burrow sediments. We also compared the U- and I-shaped part in terms of these parameters. ETSA in the burrow wall was higher than at the tidal flat surface in the warmer season, and was always higher than at surrounding non-burrow sediments. Bacterial abundance in the burrow wall was higher than at the tidal flat surface and surrounding sediment. TOC and TN contents in the burrow wall were two to three times higher than those at the tidal flat surface and non-burrow sediments, regardless of season. However, there was no significant difference in chl. a content between burrow wall and tidal flat surface. These results suggest that organic enrichment of the burrow wall is a result of organic matter particles such as phytodebris accumulation along the burrow wall. For all parameters of the burrow walls, no statistical differences were found between the two parts. Present results indicate that U. major actively transports the water containing suspended organic particles not only through the U-part but also into the deeper I-part. These indicate that burrow of the mud shrimp provides a dynamic environment for microbial community in tidal flat sediment.

Notes

Acknowledgments

The authors thank the following for their superb cooperation, without which this project and manuscript could never have been realized. Drs. T. Miyajima, H. Urakawa, A. Shibata, R. Fukuda-Sohrin and M. Shimanaga offered useful suggestions on bacteria counting, chl. a and CHN analysis, and sediment sampling. S. Arita assisted in the field observations. Y. Hasuo and S. Hasuo, superintendents of Gyotoku Bird Observatory, provided the opportunity to use the field site. Richard S. Lavin assisted in editing the English manuscript. This study was also supported by Grants-in-Aid for Scientific Research, No. 0856093, and Creative Basic Research, No. 12NP0201 (Dynamics of the Ocean Biosystem, DOBIS), of the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan. The experiments detailed in this study comply with the current laws in Japan.